LaSrMn0.5Ni0.5O4+δ: spin and oxidation state in the K2NiF4 structure
Abstract
Magnetic and structural data on the K2NiF4 structure oxide LaSrMn0.5Ni0.5O4+δare reported. Powder X-ray and electron diffraction show that the samples adopt the tetragonalI4/mmm space group without cation ordering. The absence of cation ordering together with structural considerations and magnetic data indicate that both cations are in the +III oxidation state, with high spin NiIII in contrast to both the three-dimensional perovskite LaMn0.5Ni0.5O3 and the K2NiF4 phase LaSrCr0.5Ni0.5O4 . The spin and oxidation state distributions account for the suppression of the antiferromagnetic long-range order of LaSrMnO4 and the observation of hysteresis characteristic of spin- or cluster glass behaviour below 90 K. The irreversible magnetism, but not that in the high-temperature Curie–Weiss region, is slightly altered by annealing single phase samples. The higher divergence temperature in the annealed sample is consistent with greater homogeneity of the cation distribution, as found for canonical RKKY spin glasses.